A steering apparatus for an automobile is configured as illustrated in FIG. 28 in which rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and a pair of left and right tie rods 4 are pushed or pulled in response to rotation of this input shaft 3 to thereby give a steering angle to front wheels. The steering wheel 1 is supported and fixed on the rear end section of a steering shaft 5, and this steering shaft 5, in a state of being inserted through a cylindrical steering column 6 in the axial direction, is rotatably supported on this steering column 6. Moreover, the front end section of the steering shaft 5 is connected, via a universal joint 7, to the rear end section of an intermediate shaft 8, and the front end section of this intermediate shaft 8 is connected, via another universal joint 9, to the input shaft 3.
There have been widely and conventionally known a tilting mechanism for adjusting the upper-lower position and front-rear position, and a telescopic mechanism for adjusting the front-rear position of the steering wheel 1, according to the physique or driving posture of a driver. Moreover, in the example illustrated in the drawing, there is also assembled an electrically driven power steering apparatus that reduces, with an electric motor 10 serving as an auxiliary power source, a force required for operating the steering wheel 1. Furthermore, in order to configure the above telescopic mechanism, the steering column 6 has a structure in which an outer column 11 and an inner column 12 are telescopically combined in a telescopic form, and the steering shaft 5 has a structure in which an outer tube 13 and an inner shaft 14 are torque-transmittably and telescopically combined by means of spline engagement or the like.
In the case of the tilting mechanism or the telescopic mechanism, except for ones of an electrically driven type, the position of the steering wheel 1 can be brought to an adjustable state or can be fixed in a post-adjustment position, based on an operation of an adjustment lever. As a structure for increasing a force (retentive force) for retaining the front-rear position of the steering wheel in a post-adjustment position without particularly increasing the force for operating the adjustment lever, there has been conventionally disclosed, for example as in Patent Documents 1 to 3, a structure for fixing the front-rear position of a movable column in accordance with rotation of a rod-shaped member based on an adjustment lever. In Patent Document 1 among these, there is disclosed a structure in which a movable column is nipped from both sides thereof and a non-moving column is pressed against the movable column to thereby ensure a retentive force with respect to this movable column.
FIG. 29 and FIG. 30 show such conventional structure disclosed in Patent Document 1. In the case of this conventional structure, with a cam device 16 that functions upon operation of an adjustment lever 15, it is possible to freely increase and reduce the distance between a first pressing plate 18 externally fitted on a portion close to the base end of an adjustment bolt 17, and a second pressing plate 19 externally fitted on a portion close to the tip end of this adjustment bolt 17. Moreover, a cam member 20 is externally fitted and supported on an intermediate section of this adjustment bolt 17 based on serration engagement. The tip end section of this cam member 20, through a long hole 21 formed in an intermediate section of an outer column 11a, enters into this outer column 11a, and comes in contact with the outer circumferential surface of an inner column 12a. As the adjustment lever 15 is operated, the cam device 16 reduces the distance between both of the first and second pressing plates 18 and 19, and thereby a pair of supporting plate sections 23 that constitute a nipping bracket 22 supported on a vehicle body side, is pressed against both of the side surfaces of a nipped bracket 24 fixed on the outer circumferential surface of the outer column 11a. At the same time, the tip end section of the cam member 20 presses the inner column 12a. 
In the case of such conventional structure disclosed in Patent Document 1, compared to a structure prior thereto (former structure), strength and rigidity for fixation of this front-rear position can be made higher by increasing the number of frictional engagement sections in a case of fixing the front-rear position of the steering wheel 1. That is to say, in the case of the former structure, fixation of the front-rear position of the steering wheel 1 was realized only with frictional engagement in a contact section between inner side surfaces of the pair of supporting plate sections 23 that constitute the nipping bracket 22 and both of the side surfaces of the nipped side bracket 24 fixed on the outer circumferential surface of the outer column 11a. On the other hand, in the case of the conventional structure disclosed in Patent Document 1, frictional engagement between the inner circumferential of the outer column 11a and the outer circumferential surface of the inner column 12a, associated with pressing of the cam member 20, also contributes to fixation of the front-rear position.
The tip end surface of the cam member 20 and the outer circumferential surface of the inner column 12a also come in contact with each other, however, both of these members 20 and 12a will not be displaced relatively in response to an adjustment of the front-rear position of the steering wheel 1. Therefore, contact between both of the members 20 and 12a will not contribute to increase strength and rigidity for fixation of the front-rear position.    [Patent Document 1] Japanese Patent No. 3,783,524    [Patent Document 2] Japanese Patent Application Publication No. 2007-223549    [Patent Document 3] U.S. Pat. No. 7,178,832